I have an idea for a start up, but before I get too far down the rabbit hole, I need to learn more about shipping.

I have an idea for a start up, but before I get too far down the rabbit hole, I need to learn more about shipping. The idea partially hinges on a customer shipping something to me/the business, then having me mail them something back. I'm Googling and reading about different solutions, but most seem to be about shipping to customers, and managing returns. Anyone know about resources/services/words I should use in google search to find more info or services on this? #startup #question #shipharder